[R-390] DC Fan Noise

[David Wise]

3DW7A or 3DW7D.  Tube-size COOL-RUNNING plug-n-play.
Schematics on request.  I'll sell you a programmed PIC for
the latter for $10.

73,
Dave Wise

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of n4buq at knology.net
> Sent: Friday, April 07, 2006 6:37 AM
> To: Tim Shoppa; r-390 at mailman.qth.net
> Subject: Re: [R-390] DC Fan Noise
> 
> 
> The reason the IF deck is involved is this project is a 
> replacement for the 
> ballast tube.  It is intended as a plug-n-play substitution 
> for the ballast 
> with the added advantage of having a small fan.  The fan 
> cools the dropping 
> resistors as well as anything else in its path.  If it's 
> going to be noisy, 
> though (these are new fans), then I may just have to forego 
> the fan idea.  :
> (
> 
> Barry - N4BUQ
> 
> > > I've been working on a project that will power a small 
> fan on the IF
> > deck.  
> > > I'm using the 26.2VAC supply through a single diode to a 
> 24VDC fan. 
> > This 
> > > yields about 11.5VDC (at least that's what my Fluke meter 
> shows).  I 
> > > realize this is half-wave DC so 11.5 is an "averaging" value.
> > > When I hooked it up last night, my Grundig Majestic 
> nearby picked up
> > noise 
> > > from the fan motor.
> > 
> > I think this is inevitable when you drive a commutating 
> motor (unless
> > your 24VDC fan is decades old, it is probably solid-state 
> commutation).
> > 
> > I don't think it has a lot to do with the pulsating half-sine drive.
> > 
> > An entirely different 24VDC fan may be much better or much worse,
> > hard to say without trying.
> > 
> > If you can, try to find a small AC fan. 24VAC units do 
> exist but are not
> > real common. It's vaguely possible that 24VAC may work to slowly
> > turn a 120VAC fan, but even if it'll keep it turning it 
> probably won't
> > start.
> > 
> > Big AC fans (I'm thinking of 10" or 14" rotrons etc.) work 
> OK without
> > making a lot
> > of wind noise if you use 120VAC to drive them and a 
> dropping resistor.
> > 
> > A little odd that you're aiming it at the IF deck. Yeah, 
> there's a lot
> > of
> > tubes in a small space there. I honestly do not know if 
> crumbling foam
> > in the mech filters is accelerated or not by "typical" heat 
> on the IF
> > deck.
> > 
> > Tim.
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